1. Field of the Invention
The present invention relates to a light guide plate structure and a light-guide-plate manufacturing method thereof, and more specifically, to a light guide plate structure in which refractive indexes of medium layers respectively formed on a light exit surface and a bottom surface of a light guide plate are between a refractive index of the light guide plate and a refractive index of air and a light-guide-plate manufacturing method thereof.
2. Description of the Prior Art
Please refer to FIG. 1, which is a partial sectional diagram of a keyboard 1 in the prior art. As shown in FIG. 1, the keyboard 1 includes a bottom board 10, a plurality of keyswitches 112, and a backlight module 14. Each keyswitch 12 is disposed on the bottom board 10 for a user to perform input operations. The backlight module 14 is disposed under the bottom board 10 as a light source of the keyboard 1. The backlight module 14 includes a light shielding board 140, a light guide plate 142, a metal board 144, a reflection sheet 146, and a light emitting unit 148. The light shielding board 140 is disposed under the bottom board 10. The light guide plate 142 is disposed under the light shielding board 140. The metal board 144 is disposed under the light guide plate 142. The reflection sheet 146 is disposed on the metal board 144 and located under the light guide plate 142. The light emitting unit 148 is disposed at a side of the light guide plate 142. In such a manner, light could be evenly emitted out of the light guide plate 142 by total reflection of light occurring in the light guide plate 142 and reflection of the reflection sheet 146, and then be projected out of the keyswitches 12 after passing through the light shielding board 140 toward the bottom board 10. Accordingly, the purpose that the keyboard 1 could emit light is achieved.
In the aforesaid design, the total reflection of light could be generated by the design in which a refractive index of the light guide plate 142 is greater than a refractive index of air (i.e. 1) located between the light shielding board 140 and the light guide plate 142. However, since a surface of the light guide plate 142 is not protected appropriately, pollution of the surface of the light guide plate 142 due to attachment or scratch of foreign matter (e.g. grease or dust) may occur during the process of assembling the light guide plate 142 in the keyboard 1, so as to frustrate the total reflection of light in the light guide plate 142. Thus, it may cause the light leakage problem or reduce the travel distance of light in the light guide plate 142, so that the light use efficiency and illumination uniformity of the light guide plate 142 could be influenced. Furthermore, as shown in FIG. 1, the backlight module 14 utilizes the design in which the light guide plate 142 is disposed between the light shielding board 140 and the reflection sheet 146, to guide light to be evenly projected out of the keyswitches 12. However, since disposal of the light guide plate 142, the light shielding board 140 and the reflection sheet 146 may occupy excessive inner space of the keyboard 1, the aforesaid design is disadvantageous to the thinning design of the keyboard 1.